/*
******************************************************************************
*
*   Copyright (C) 1999-2006, International Business Machines
*   Corporation and others.  All Rights Reserved.
*
******************************************************************************
*   file name:  utf_impl.c
*   encoding:   US-ASCII
*   tab size:   8 (not used)
*   indentation:4
*
*   created on: 1999sep13
*   created by: Markus W. Scherer
*
*   This file provides implementation functions for macros in the utfXX.h
*   that would otherwise be too long as macros.
*/

#include "icu_utf.h"

namespace base_icu
{

    /**
    * UTF8_ERROR_VALUE_1 and UTF8_ERROR_VALUE_2 are special error values for UTF-8,
    * which need 1 or 2 bytes in UTF-8:
    * \code
    * U+0015 = NAK = Negative Acknowledge, C0 control character
    * U+009f = highest C1 control character
    * \endcode
    *
    * These are used by UTF8_..._SAFE macros so that they can return an error value
    * that needs the same number of code units (bytes) as were seen by
    * a macro. They should be tested with UTF_IS_ERROR() or UTF_IS_VALID().
    *
    * @deprecated ICU 2.4. Obsolete, see utf_old.h.
    */
#define CBUTF8_ERROR_VALUE_1 0x15

    /**
    * See documentation on UTF8_ERROR_VALUE_1 for details.
    *
    * @deprecated ICU 2.4. Obsolete, see utf_old.h.
    */
#define CBUTF8_ERROR_VALUE_2 0x9f


    /**
    * Error value for all UTFs. This code point value will be set by macros with e>
    * checking if an error is detected.
    *
    * @deprecated ICU 2.4. Obsolete, see utf_old.h.
    */
#define CBUTF_ERROR_VALUE 0xffff

    /*
    * This table could be replaced on many machines by
    * a few lines of assembler code using an
    * "index of first 0-bit from msb" instruction and
    * one or two more integer instructions.
    *
    * For example, on an i386, do something like
    * - MOV AL, leadByte
    * - NOT AL         (8-bit, leave b15..b8==0..0, reverse only b7..b0)
    * - MOV AH, 0
    * - BSR BX, AX     (16-bit)
    * - MOV AX, 6      (result)
    * - JZ finish      (ZF==1 if leadByte==0xff)
    * - SUB AX, BX (result)
    * -finish:
    * (BSR: Bit Scan Reverse, scans for a 1-bit, starting from the MSB)
    *
    * In Unicode, all UTF-8 byte sequences with more than 4 bytes are illegal;
    * lead bytes above 0xf4 are illegal.
    * We keep them in this table for skipping long ISO 10646-UTF-8 sequences.
    */
    const uint8 utf8_countTrailBytes[256] =
    {
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
        0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,

        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,
        1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1, 1,

        2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2, 2,
        3, 3, 3, 3, 3,
        3, 3, 3,    /* illegal in Unicode */
        4, 4, 4, 4, /* illegal in Unicode */
        5, 5,       /* illegal in Unicode */
        0, 0        /* illegal bytes 0xfe and 0xff */
    };

    static const UChar32 utf8_minLegal[4] ={ 0, 0x80, 0x800, 0x10000 };

    static const UChar32 utf8_errorValue[6] =
    {
        CBUTF8_ERROR_VALUE_1, CBUTF8_ERROR_VALUE_2, CBUTF_ERROR_VALUE, 0x10ffff,
        0x3ffffff, 0x7fffffff
    };

    /*
    * Handle the non-inline part of the U8_NEXT() macro and its obsolete sibling
    * UTF8_NEXT_CHAR_SAFE().
    *
    * The "strict" parameter controls the error behavior:
    * <0  "Safe" behavior of U8_NEXT(): All illegal byte sequences yield a negative
    *     code point result.
    *  0  Obsolete "safe" behavior of UTF8_NEXT_CHAR_SAFE(..., FALSE):
    *     All illegal byte sequences yield a positive code point such that this
    *     result code point would be encoded with the same number of bytes as
    *     the illegal sequence.
    * >0  Obsolete "strict" behavior of UTF8_NEXT_CHAR_SAFE(..., TRUE):
    *     Same as the obsolete "safe" behavior, but non-characters are also treated
    *     like illegal sequences.
    *
    * The special negative (<0) value -2 is used for lenient treatment of surrogate
    * code points as legal. Some implementations use this for roundtripping of
    * Unicode 16-bit strings that are not well-formed UTF-16, that is, they
    * contain unpaired surrogates.
    *
    * Note that a UBool is the same as an int8_t.
    */
    UChar32 utf8_nextCharSafeBody(const uint8 *s, int32 *pi, int32 length,
        UChar32 c, UBool strict)
    {
        int32 i=*pi;
        uint8 count=CBU8_COUNT_TRAIL_BYTES(c);
        if((i)+count<=(length)) {
            uint8 trail, illegal=0;

            CBU8_MASK_LEAD_BYTE((c), count);
            /* count==0 for illegally leading trail bytes and the illegal bytes 0xfe and 0xff */
            switch(count)
            {
                /* each branch falls through to the next one */
            case 5:
            case 4:
                /* count>=4 is always illegal: no more than 3 trail bytes in Unicode's UTF-8 */
                illegal=1;
                break;
            case 3:
                trail=s[(i)++];
                (c)=((c)<<6)|(trail&0x3f);
                if(c<0x110) {
                    illegal|=(trail&0xc0)^0x80;
                } else {
                    /* code point>0x10ffff, outside Unicode */
                    illegal=1;
                    break;
                }
            case 2:
                trail=s[(i)++];
                (c)=((c)<<6)|(trail&0x3f);
                illegal|=(trail&0xc0)^0x80;
            case 1:
                trail=s[(i)++];
                (c)=((c)<<6)|(trail&0x3f);
                illegal|=(trail&0xc0)^0x80;
                break;
            case 0:
                if(strict>=0) {
                    return CBUTF8_ERROR_VALUE_1;
                } else {
                    return CBU_SENTINEL;
                }
                /* no default branch to optimize switch()  - all values are covered */
            }

            /*
            * All the error handling should return a value
            * that needs count bytes so that UTF8_GET_CHAR_SAFE() works right.
            *
            * Starting with Unicode 3.0.1, non-shortest forms are illegal.
            * Starting with Unicode 3.2, surrogate code points must not be
            * encoded in UTF-8, and there are no irregular sequences any more.
            *
            * U8_ macros (new in ICU 2.4) return negative values for error conditions.
            */

            /* correct sequence - all trail bytes have (b7..b6)==(10)? */
            /* illegal is also set if count>=4 */
            if(illegal || (c)<utf8_minLegal[count] || (CBU_IS_SURROGATE(c) && strict!=-2)) {
                /* error handling */
                uint8 errorCount=count;
                /* don't go beyond this sequence */
                i=*pi;
                while(count>0 && CBU8_IS_TRAIL(s[i])) {
                    ++(i);
                    --count;
                }
                if(strict>=0) {
                    c=utf8_errorValue[errorCount-count];
                } else {
                    c=CBU_SENTINEL;
                }
            } else if((strict)>0 && CBU_IS_UNICODE_NONCHAR(c)) {
                /* strict: forbid non-characters like U+fffe */
                c=utf8_errorValue[count];
            }
        } else /* too few bytes left */ {
            /* error handling */
            int32 i0=i;
            /* don't just set (i)=(length) in case there is an illegal sequence */
            while((i)<(length) && CBU8_IS_TRAIL(s[i])) {
                ++(i);
            }
            if(strict>=0) {
                c=utf8_errorValue[i-i0];
            } else {
                c=CBU_SENTINEL;
            }
        }
        *pi=i;
        return c;
    }

} //namespace base_icu